“Schools with a number of weaker pupils, who relied more heavily on coursework in the past, may find their results plummeting,” Mr Lenon told The Daily Telegraph.

"Now, the fact is that many pupils get their best mark in their teacher assessed coursework. Where a school has a significant number of more marginal pupils who historically got over the pass/fail boundary as a result of their high coursework marks, clearly those are the schools who might suffer from these reforms.”

“What they mean is across the country as a whole the grade distribution will be similar to last year,” Mr Lenon said. “That won’t be the same for individual schools. Some will do better and some worse."

He said one reason for a school doing better is down to teachers being better prepared to teach the new courses. Meanwhile, some schools may achieve worse results due to coursework being “stripped out” of many core subjects.

“If you were a school that relied heavily on very good coursework – and they may well be coursework marks that they deserved, [students] may be well trained and earned those marks – that will no longer be available to them," Mr Lenon said.

“There was the potential for unfairness. Some teachers could be giving more help [with coursework] than others.”

Schools with a number of weaker pupils, who relied more heavily on coursework in the past, may find their results plummetingBarnaby Lenon, chair of the ISC

Many will be the first cohort to take the new GCSEs, which were reformed by former Education Secretary Michael Gove as part an attempt to inject rigour into the qualifications and bring the UK in line with top performing countries in the Far East.

Of the 5.1 million exams that were taken this summer, 90 per cent were in the new reformed subjects which use a numerical grading system of 9 to 1 instead of A* to G.

Many of the reformed GCSEs have had their coursework element vastly reduced or axed altogether. Coursework – or “non examined assessment” – used to make up 40 per cent English literature and English language but now it has been reduced to zero.

Barnaby Lenon is the former headmaster at Harrow SchoolCredit:
PAUL GROVER

History, geography, biology, chemistry and physics used to each have 25 per cent coursework, all of which has been taken out of the reformed qualifications.

Meanwhile, French, Spanish and German have all had their coursework elements reduced from 60 to 25 per cent.

An Ofqual spokesman said that coursework was “constraining teaching” in many subjects and failed to adequately discriminate between students’ abilities. “We designed the assessment of reformed qualifications to address these shortcomings, as well as reflect the balance and nature of the new subject content,” the spokesman said.

“This has led to a reduction in coursework in many subjects, but it has been retained or even increased where it is necessary for valid assessment.

“Where coursework is now used, there are safeguards around its operation, for example, limiting the time tasks are available for completion and requiring external marking of work in some subjects.”